During most of this century, hard gelatin capsules were a popular dosage form for prescription and over-the-counter (OTC) drugs. The ability to combine capsule halves having different colors provided manufacturers with a unique means of distinguishing various pharmaceutical products. Many patients preferred capsules over tablets, perceiving them as being easier to swallow. This consumer preference prompted pharmaceutical manufacturers to market certain products in capsule form even when they were also available in tablet form.
Generally, empty hard gelatin capsules are manufactured using automated equipment. This equipment employs rows of stainless steel pins, mounted on bars or plates, which are dipped into a gelatin solution maintained at a uniform temperature and fluidity. The pins are then withdrawn from the gelatin solution, rotated, and then inserted into drying kilns through which a strong blast of filtered air with controlled humidity is forced. A crude capsule half is thus formed over each pin during drying. Each capsule half is then stripped, trimmed to uniform length, filled and joined to an appropriate mating half.
An alternative to capsule products are caplets, which are solid, oblong tablets that may be coated with various polymers such as cellulose ethers to improve their aesthetics, stability, and swallowability. Typically, such polymers are applied to the tablets either from solution in organic solvents, or from aqueous dispersion via spraying. However, such spray-coated tablets lack the shiny surface and elegance of the hard gelatin capsules. Additionally, it is not commercially feasible to spray-coat a tablet with a differant color coating on each end
Another alternative to capsule products are “gelcaps,” which are elegant, shiny, consumer-preferred dosage forms that are prepared by dipping each half of an elongated tablet in two different colors of gelatin solution. See U.S. Pat. Nos.: 4,820,524; 5,538,125; 5,685,589; 5,770,225; 5,198,227; and 5,296,233, which are all incorporated by reference herein. A similar dosage form, commercially available as a “geltab,” is prepared by dipping each half of a round, convex tablet into different colors of gelatin solution, as described in U.S. Pat. No. 5,228,916, U.S. Pat. No. 5,436,026 and U.S. Pat. No. 5,679,406, which are all incorporated by reference herein. As used herein, such “gelcaps” and “geltabs” shall be included within the broader term, “tablets.”
However, the use of gelatin as a pharmaceutical coating material presents certain disadvantages and limitations, including the potential for decreased dissolution rate after extended storage due to cross-linking of the gelatin, potential for microbial contamination of the gelatin solution during processing, and long processing times due to extensive drying requirements. Further, the energy-related costs associated with gelatin coatings tend to be high since the gelatin material is typically applied to the substrates at an elevated temperature of at least about 40° C. in order to maintain fluidity of the gelatin, while the substrates are maintained at about 50° C. in order to minimize microbial growth.
Various attempts have been made to produce gelatin-free hard shell capsules. For example, WO 00/18835 discloses the combination of starch ethers or oxidized starch and hydrocolloids for use in preparing hard capsule shells via conventional dip molding processing. See also U.S. Pat. No. 4,001,211 (capsules prepared via pin dip coating with thermogelled methylcellulose ether compositions). However, due to potential tampering concerns, hard gelatin capsules are no longer a preferred delivery system for consumer (over-the-counter) pharmaceuticals, dietary supplements, or other such products. Additionally, the properties of an ideal composition into which steel pins are to be dipped then dried to form hard capsule shells thereon are not necessarily the same as those for dipping tablets to form a coating thereon. For example, relevant physical properties such as viscosity, weight-gain, film thickness, tensile strength, elasticity, and moisture content will differ between compositions for hard capsule formation and for coating tablets. See e.g., U.S. Pat. No. 1,787,777 (Optimal temperatures of the substrate and coating solution, residence times in the solution, and drying conditions differ.)
One disadvantage associated with dipping tablets or capsules into a non-gelatin coating system is that the resulting coatings often lack adequate tensile strength, plasticity, hardness, and thickness. Moreover, the inclusion of plasticizers into such non-gelatin coating systems often results in tablets having soft, tacky coatings without a hardness sufficient to maintain their shape or smoothness during handling. In addition, many non-gelatin compositions do not adhere to the tablet substrate in an amount sufficient to uniformly cover the tablet after a single dipping. Further, many non-gelatin compositions lack the sufficient rheological properties necessary to maintain uniform color dispersion throughout the dipping and drying process. Although attempts have been made to improve the rheological properties of these compositions by, for example, increasing their solids content in order to increase viscosity. However, such compositions often disadvantageously resulted in undesirable coating aesthetics such as surface roughness, decreased gloss, and non-uniform coating thickness.
It is desirable to find a coating material, and in particular a dip coating material, which not only produces a similar elegant, shiny, high gloss, consumer-preferred dosage form similar to that of gelatin-coated forms, but which is absent the limitations of gelatin, particularly those noted above.